[PATCH] mm: add a note about partially hardcoded VM_* flags (7e2cff42) · Commits · 戴 / test

Hugh made me note this line for permission checking in mprotect(): if ((newflags & ~(newflags >> 4)) & 0xf) { after figuring out what's that about, I decided it's nasty enough. Btw Hugh itself didn't like the 0xf. We can safely change it to VM_READ|VM_WRITE|VM_EXEC because we never change VM_SHARED, so no need to check that. Signed-off-by:

Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it> Acked-by:

Hugh Dickins <hugh@veritas.com> Signed-off-by:

Andrew Morton <akpm@osdl.org> Signed-off-by:

Linus Torvalds <torvalds@osdl.org>

include/linux/mm.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -136,6 +136,7 @@ extern unsigned int kobjsize(const void *objp);
		#define VM_EXEC 0x00000004
		#define VM_SHARED 0x00000008

		/* mprotect() hardcodes VM_MAYREAD >> 4 == VM_READ, and so for r/w/x bits. */
		#define VM_MAYREAD 0x00000010 /* limits for mprotect() etc */
		#define VM_MAYWRITE 0x00000020
		#define VM_MAYEXEC 0x00000040

mm/mprotect.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -248,7 +248,8 @@ sys_mprotect(unsigned long start, size_t len, unsigned long prot)

		newflags = vm_flags \| (vma->vm_flags & ~(VM_READ \| VM_WRITE \| VM_EXEC));

		if ((newflags & ~(newflags >> 4)) & 0xf) {
		/* newflags >> 4 shift VM_MAY% in place of VM_% */
		if ((newflags & ~(newflags >> 4)) & (VM_READ \| VM_WRITE \| VM_EXEC)) {
		error = -EACCES;
		goto out;
		}

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